In many transmission systems, both the receiver and transmitter include a clock that controls various activities. The clock is typically a crystal oscillator that controls processing-related activities associated with transmitting and receiving data over a channel. Due to minor variations in the clocks, the receiver and transmitter clocks are often offset from each other, i.e., the frequency of the clock at the receiver is often different from that at the transmitter.
One problem associated with mismatched clock frequencies is that the receiver may be unable to recover the transmitted signal without errors. For example, a discrete multitone (DMT) transmission system may transmit data over 256 distinct carriers (also referred to as tones) with each carrier being separated by 4.3125 KHz. When the transmitting and receiving clocks are mismatched, received tones may leak into one another. This is known as Intercarrier Interference (ICI). When the ICI is particularly high, the receiver may be unable to recover the transmitted signal without errors.